This invention relates to fluid operated friction torque transmitting devices and more particularly to such devices having a variable torque capacity.
It is known that directional torque sensitivity can be provided within a clutch or brake arrangement to sense torque reversal during a ratio interchange in a power transmission. During the ratio interchange, torque is transferred from an off-going friction device to an on-coming friction device. As the torque capacity increases at the on-coming friction device, the off-going friction device will undergo a decrease in torque transmission and will experience a negative or torque reversal if not released at the proper time. If the desired shift timing is not accomplished; i.e., torque reversal occurs, a transient force termed "shift shock" will occur.
The shift timing has generally been accomplished through the use of one-way type devices which are designed to transmit torque in only one direction. These devices do, however, add cost and complexity to the transmission. If a brake member is to be the off-going device during a ratio interchange, it is possible to use a band type brake, especially a multiwrap type, to provide some directional sensitivity to torque transmissions. These devices also have limitations in their design and operation which make them less than the ideal solution to the problem. This directional torque sensitivity is fixed and is not sensitive to load or speed.
In rotating type clutches, it has been proposed to use a directional sensitive valve member which is operable to exhaust the clutch apply chamber during a torque reversal. These types of devices have been proposed for torque converter clutch mechanisms to permit disengagement of the torque converter clutch when the operator changes from a driving to a coasting condition. Devices of this type can be seen in U.S. Pat. No. 3,734,251 issued May 22, 1973, to Annis et al. and U.S. Pat. No. 3,410,378 issued Nov. 12, 1968, to Maurice.